1. Field of the Invention
The field of the invention pertains to sealing devices for use in a downhole environment, specifically, for sealing against a fiber optic cable.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion in this section.
In many well related operations, fiber optic control lines are used to establish communication with and to control downhole components. For example, fiber optic distributed temperature sensors may be used to measure the temperature along the entire length of a wellbore as well as communicate the temperature data to the surface of the well. However, sealing the fiber optic line portion of the fiber optic cable against severe well pressures and environmental conditions can be challenging. A repeatable balance must be established between providing a seal against the fiber optic line without applying so much force that the fiber optic line is subsequently damaged.
In conventional applications, an end cap may be secured to a housing in order to provide a compressive force on a cable or control line passing there through. The compressive force may be controlled though precise control of the torque applied to the end cap and/or accurate predictions of the occupying space of the cable seal when the end cap is fully tightened. However, most metal or shielded cables and control lines are tolerant of a wide range of compressive pressures. Accordingly, cables and control lines may be rapidly sealed through the use of less precisely controlled processes without risk of a subsequent increase in the potential for damaging cables and control lines.
On the other hand, fiber optic cables are much more susceptible to damage resulting from the application of too large of a compressive force. The fragile nature and the miniature size of the fiber optic line requires more control than typically used in sealing a control line. In the field, precisely controlling the torque so as to avoid compressive damage to a fiber optic cable may be costly and time consuming. In addition, in order to accurately determine the shape and quantity of the sealing material and housing so as to provide a sufficient compressive force while still allowing for a securing torque for the end cap requires extensive modeling and/or testing of various configurations for a range of operating conditions. In some cases, fiber optic lines are sealed using epoxy between the fiber and the barrier.